As broadcasters continue the transition from analog to digital video, the television production process is increasingly conducted in an all-digital domain, that is, from the initial camera shot to the display in the consumer's living room. Compressed digital content is stored as large media files on server networks and produced in a wide variety of file formats, standards and compression algorithms. In such an environment, quality control operators are under increasing pressure to ensure the integrity of digital files before playback, and therefore that the video content is reaching viewers with a desired quality level.
One problem that can occur when using interlaced video is that of field inversion. More particularly, interlaced video is arranged in successive frames, where each frame includes two fields. One field is made up of the odd horizontal lines in a frame, and it is called the odd field or top field since it contains the top line of the image. The other field is made up of the even horizontal lines in a frame, and it is called the even field or bottom field. When interlaced data is displayed, the odd/top field is displayed first followed by the even/bottom field to complete the frame.
While television and interlaced video signals typically have a flag associated therewith to indicate which field is which (i.e., top or bottom), the flag can sometimes inadvertently get changed during the encoding process. Similarly, when combining video from different sources, it is possible that an interlaced video feed may become inverted, i.e., the top and bottom frames are not displayed in the proper order. When this happens, the viewer will typically see artifacts or “ghosts” in the displayed video, as the fields are being displayed in reverse chronological order with fields occurring later in time (i.e., the even fields) being displayed before fields (i.e., the odd fields) that come earlier in time. Yet, to ensure that such a field inversion does not occur in a video playback, an operator is typically required to manually view all or part of the video feed to spot the undesired artifacts, which may be time consuming, cumbersome, and potentially error prone depending upon the skill of the operator.
Various approaches have been developed to alleviate the field inversion problem. One example is disclosed in U.S. Pat. No. 4,724,487 which discloses a picture-in-picture image signal generator that includes a source of an auxiliary video signal and an auxiliary synchronization component separator which produces an auxiliary odd/even field signal. Auxiliary image data is stored in a memory for subsequent retrieval. A source of a main video signal and associated synchronization component separator, which produces a main odd/even field signal, is also provided. A signal combiner combines a portion of the main video signal with data retrieved from the memory to form a picture-in-picture video signal. Furthermore, an interlace inversion detector generates a signal indicating an interlace inversion condition in response to the main and auxiliary odd/even field signals, and a correction to the interlacing is made in response to the interlace inversion signal.
Despite the existence of such systems, further advancements in interlace video field inversion detection may be desired to alleviate the burden on video quality control operators that the detection and correction of this problem may cause.